August 31, 2010 9 Comments
The Meteor Activity Outlook is a weekly summary of expected meteor activity written by Robert Lunsford, Operations Manager of the American Meteor Society and contributor to this blog. The original unedited version of this week’s Meteor Activity Outlook can be found at the American Meteor Society’s site.
September offers longer nights in the northern hemisphere that tend to be less hazy than those experienced in mid-summer. In the sky, no major showers are visible from either hemisphere but the northern hemisphere enjoys the advantage of higher sporadic rates. Most of the shower activity this month is produced from the Perseus-Aurigid complex active this time of year. These showers rarely produce more than five meteors per hour but still manage to produce most of the shower activity seen this month. Unfortunately the Perseus-Aurigid complex lies too low in the northern sky for southern hemisphere observers to view very well. Video studies have shown that the Southern Taurids are visible as early as September 7th therefore after this date the Antihelion radiant will no longer be listed until the Taurid showers end in December. The Antihelion meteors are still active but their radiant is superimposed upon that of the more numerous Taurids, therefore it is impossible to properly separate these meteors. Observers in the southern hemisphere suffer from some of their lowest rates of the year this month. The Southern Taurid radiant is not too badly placed so observers south can expect to see a little of this activity this month.
During this period the moon reaches its last quarter phase on Wednesday September 1st. At this time the moon will be located ninety degrees west of the sun and will rise near 0100 local daylight time (LDT) for locations in the mid-northern latitudes of the northern hemisphere. This weekend the waning gibbous moon will rise during the late evening hours and remain in the sky the remainder of the night. Meteor observations are difficult under such circumstances unless your sky is transparent. The estimated total hourly rates for evening observers this week is ~3 from the northern hemisphere and ~2 from the southern hemisphere. For morning observers the estimated total hourly rates should be ~12 from the northern hemisphere and ~8 as seen from the southern hemisphere. The actual rates will also depend on factors such as personal light and motion perception, local weather conditions, alertness and experience in watching meteor activity. During this period, moonlight reduces activity seen during the morning hours.
The radiant positions and rates listed below are exact for Saturday night/Sunday morning August 28/29. These positions do not change greatly day to day so the listed coordinates may be used during this entire period.
As seen from the mid-northern hemisphere (45N) one would expect to see approximately five sporadic meteors per hour during the last hour before dawn as seen from rural observing sites. Evening rates would be near two per hour. As seen from the mid-southern hemisphere (45S), morning rates would be near fourteen per hour as seen from rural observing sites and three per hour during the evening hours. Locations between these two extremes would see activity between the listed figures. Morning rates are slightly reduced due to moonlight.
The following showers are expected to be active this week:
August Draconids (AUD)
The last few remnants from the August Draconids (AUD) may be seen this weekend. The radiant is currently located at 18:44 (281) +63. This position lies in southern Draco, ten degrees east of the second magnitude star Eltanin (Gamma Draconis). With an entry velocity of 23 km/sec. most of these meteors will appear to move slowly. The radiant is best placed near 2200 Local Daylight Time (10pm LDT) when it lies highest in the sky. Due to its high northern declination this shower is not well seen from the southern hemisphere.
The wide Antihelion (ANT) radiant is now centered at 23:12 (348) -03. This area of the sky lies in western Pisces, three degrees north of the fourth magnitude star Phi Aquarii. This radiant is best placed near 0200 LDT when it lies on the meridian and is located highest in the sky. Due to the large size of this radiant, any meteor radiating from eastern Aquarius, southern Pegasus, western Pisces, or western Cetus could be a candidate for this shower. Rates at this time should be ~2 per hour no matter your location. With an entry velocity of 30 km/sec., the average Antihelion meteor would be of medium-slow speed.
Alpha Aurigids (AUR)
The Alpha Aurigids (AUR) is the first radiant of the Perseus-Aurigid complex to become active. Maximum occurs on September 1, so rates this weekend will be very low. Even at maximum with a last quarter moon in the sky, rates will most likely not exceed one shower member per hour. The radiant position at maximum is 06:04 (091) +36. This position lies in eastern Auriga only one degree southeast of the third magnitude star Theta Aurigae. This is different than the old position which was close to Capella (Alpha Aurigae). Video results from the 2007 outburst of this shower showed that a majority of the activity came from the radiant near Theta Aurigae. The radiant is best placed near 0500 LDT, when it lies highest in a dark sky. With an entry velocity of 67 km/sec., most activity from this radiant would be swift. Activity can be seen, if it occurs, from the southern tropic regions during the last few hours before dawn.
The list below presents a condensed version of the expected activity this week. Rates and positions are exact for Saturday night/Sunday morning.
Shower Name RA DEC Vel Rates km/s NH SH AUG August Draconids 18h 44m +63 23 <1 <1 ANT Antihelions 23h 12m -03 30 2 3 AUR Alpha Aurigids 06h 04m +36 67 1 <1 RA - Right Ascension DEC - Declination Vel - Velocity relative to Earth (in km per sec) Rates - Rate of visible meteors per hour from a dark site NH - Northern Hemisphere SH - Southern Hemisphere